Compositions stabilized with hydroxyindole



COMPOSITIONS STABILIZED WITH HYDROXYlNDOLE Alan Bell and Gerald R.Lappin, Kingsport, Tenn., as-

signors to Eastman'Kodak Company, Rochester, N. Y., a corporation of NewJersey No Drawing. Application February 24, 1954, Serial No. 412,373

12 Claims; (Cl. 99-163) This invention relatesto antioxidantcompositions and to oxidizable-materials stabilized therewith, and isparticularly concerned with antioxidants comprising S-hydroxyindolecompounds and to oxidizable compositions containing stabilizing amountsof such antioxidants.

A large number of materialsincluding fats, oils, and hydrocarbons suchas gasoline and the like are normally subject to the deleterious effectsof oxidation upon storage. As a consequence, it is usually desirable toincorporate in such oxidizable materials a small amount of a stabilizingmaterial which is efiective to reduce the oxidation to anunobjectionable level. A large number of stabilizers have been proposedfor use alone or in various combinations. Among the stabilizers whichhave been tried for such applications are the p-hydroxy aromatic aminessuch as p-amino phenol. These materials exhibit a high antioxidantpotency but suffer the serious disadvantage of being subject toair'oxidation themselves and hence of being too unstable for practicaluse in most cases.

It is accordingly an object of this invention to provide a new andimproved class of antioxidants which cornbine the high degree ofantioxidant potency which is characteristic of p-hydroxy aromatic amineswith an unusual degree of stability to oxidation themselves.

Another object of the invention is to stabilize normally oxidizablematerials such as fats, oils, and hydrocarbons againstobjectionableoxidation'by the incorporation therein of a'hitherto unknown type ofantioxidant.

Another object of the invention is to facilitate the storage ofmaterialswhich' are normally subject to the deleterious eifects ofoxidation by providing a highly effective class of antioxidantscomprising S-hydroxyindoles.

Another object of the invention is to provide new and improvedantioxidant compositions of widespread utility.

Other objects will be apparent from the description and claims whichfollow.

These and other objects'are' attained by means of this invention, whichcomprises stabilizing normally oxidizable material with an antioxidantcomposition embodying this invention and comprising a S-hydroxyindole ofthe formula wherein R1 is either hydrogen or an alkyl group and R2, R3,R4, R5 and Re are either hydrogen, alkyl, aryl, hydroxyl or aminogroups. These antioxidants can be used alone or in admixture with othersimilar or dissimilar The antioxidants of this invention arecharacterized by having the indole structure with'ahydroxylsubstituent'in the 5 position. The hydroxyindoles of this kind'can' besubstituted in any one-or more .of the 2, 3,.4, 5 andfi positionswithout negativing the antioxidant potency of the material. In this waya large number of nuclearl'y substituted S-hydroxyindoles' can be usedwith essentially the same degree of eflectiveness. The compounds whichare of particular utility in practicing the invention are the. nuclearlyalkylated S-hydroxyindoles wherein each alkyl group contains from 1 to 4carbon atoms. Optimum results are obtained when thenuclearfsub'stituents ar kept at a minimum level. Thus the-loweralkyl-sub'sti tuted S-hydroxyindoles are preferred in practicing-the invention, and the 2-alkyl and 2,6-dialkyl 5-hydroxyindoles are ofparticular utility.

The antioxidant compositions of this invention can be prepared in anydesired manner. A highly successful method for preparing hydroxyindolesis the process de'. scribed in the copending application of John F.Tinker; Serial No. 389,885, filed November 2, 1953. By the processtherein described, indoles are readily prepared by the simple processofheating a mixture of Raney nickel and a Z-amino phenol alkanol wherebyan indole is formed by concomitant dehydration and cyclization of thealkanol. This process is illustrated by Equation I.

Equation I In Equation I, R1 represents either hydrogen or an alkylgroup which is preferably a lower alkyl group of from 1 to 4- carbonatoms, R2, R3, R4, R5 and Rs are either hydrogen or an alkyl, aryl,hydroxyl or amino group.

An alternative method of preparing the compounds embodying thisinvention comprises "the reaction as illustrated in Equation II asfollows:

In Equation II, R1, R2, R3, R4, R5 and Re have the values assigned inthe previous formulas.

The process is readily effected by heating a mixture of the quinone orsubstituted quinone together with the amino acid in a suitable solventwhereby a S-hydroXyindole carboxylate is formed. This carboxylate canthereafter be hydrolyzed and decarboxylated simultaneously with aqueousalkali and then acidified to give the corresponding S-hydroxyindole(including the substituted 5- hydroxyindoles as defined herein). Theantioxidants prepared in accordance with this invention can be used forstabilizing any of the materials which are normally subject tooxidation. Thus, for example, these stabilizers are very effective foruse in stabilizing fatty materials such as the glycerides, and includingboth the solid fats and the fatty oils. Thus they can be employed forstabilizing animal fats such as lard and the like, as well as vegetableoils such as cottonseed. oil, soybean .oil, cocoanut oil, corn oil,peanutoil, and the like, aswell as free fatty acids such as oleicacid,and similar readily oxidizable fatty acids. In a similar manner thecompounds of this invention can be used for stabilizing oxidizablehydrocarbons such as cracked gasoline and similar petroleum derivatives,as well as rubber and other oxidizable ma terials.

The amount of antioxidant which is employed in practicing this inventioncan be varied depending upon the material being stabilized, the degreeof stabilization desired, the presence or absence of other stabilizingmaterials and similar variable factors. In most cases, the stabilizersare employed in concentrations of from about 0.005% to about 0.5% byweight based on the total weight of the composition being stabilized.Larger amounts such as amounts of as much as 1% or 2% or larger can beemployed without deleterious effects, but such larger amounts areusually not necessary for optimum stabilization. Generally the compoundscontaining the least nuclear substituents can be employed in the lowestamounts since their activity appears to be somewhat higher than the morehighly substituted compounds.

The preparation of typical compounds embodying this invention isillustrated by the following examples. Other compounds within the scopeof the invention can be prepared in a similar manner as describedherein, and it is not intended that the invention shall be limited tothe specific compounds which are included for purposes of illustration.

EXAMPLE 1 Forty-three g. (0.4 mole) of quinone was dissolved in 500 ml.of acetone at 50 C. The resulting solution was added in portions to asolution of 51 g. (0.4 mole) of ethyl fi-aminocrotonate in 50 ml. ofacetone. The mixture was refluxed for 3 hours and then diluted with 100ml. of water to give, after filtration, 34 g. of ethyl 5- hydroxy 2'methylindole 3 carboxylate. This ester was simultaneously hydrolyzed anddecarboxylated by heating it with aqueous sodium hydroxide. Theresulting produce was then acidified and filtered to give g. of5-hydroxy-2-methylindole.

EXAMPLE 2 An alternative method of preparing 5-hydroxy-2- methylindolewas eifected by heating p-(2-chloroallylamino) phenol in an autoclavewith hydrogen fluoride. By this method a poor yield ofS-hydroxy-Z-methylindole Was obtained.

EXAMPLE 3 Equimolar proportions of toluquinone and ethyl B- with water.The produce was hydrolyzed wtih aqueous alkali and acidified to give agood yield of 5-hydroxy-2, 6-dimethylindole.

The other substituted S-hydroxyindoles included within the invention canbe prepared in a similar manner by the choice of a suitably substitutedquinone and a suitable amino acid as set out in Equation II. In likemanner, the hydroxyindoles of this invention can be prepared by a simpleheating with Raney nickel according to the process shown in Equation 1.

The utility of a typical S-hydroxyindole in stabilizing gasoline isillustrated in the following example. The stabilization was testedaccording to the Active Oxygen Method (AOM), whereby air was bubbledthrough a sample of the stabilized composition and the time necessaryfor the sample to reach a peroxide content of milliequivalents perkilogram was measured.

4 EXAMPLE 4 antioxidants of this invention in fatty compositions which'aminocrotonate were refluxed in acetone and then diluted I are normallysubject to the development of rancidity. The results of a typical testin which lard was used as the substrate are set out in the followingexample.

, EXAMPLE, 5

Typical samples of lard were stabilized with equal amounts of butylatedhydroxyanisole, and two typical antioxidants of this invention. Theresulting compositions were then subjected to the A. O. M. test andcompared with an unstabilized sample of lard. The results obtained areset out in Table 1. The data listed in the column headed A. O. M.represents the number of hours which were necessary to reach a peroxidevalue of 20. The last column in the test represents an antioxidant indexwherein the compositions embodying this invention were compared with thebutylated hydroxyanisole composition as a standard.

Table 1 Concentration,

Antioxidant percent As can be seen from the table, greatly improvedstabilities were obtained according to this invention. In utilizing thecompounds of this invention, it may be de sirable in some cases toemploy mixtures of one or more of such compounds with other antioxidantmaterials such as butylated hydroxyanisole, tocopherol, or similar wellknown antioxidants, with or without the simultaneous use of synergizingacid such as citric acid 'or ortho phosphoric acid. Such compositionscontaining one or more other antioxidant materials in cobination withthe antioxidants of this invention are considered to be within the scopeof the invention. Such antioxidant compositions can also include asuitable vehicle which can be a fat, fatty oil, glyceride partial ester,or a solvent if desired.

The invention has been described in considerable detail with particularreference to certain preferred embodiments thereof. It will beunderstood, however, that variations and modifications can be effectedwithout departing from the spirit and scope of the invention asdescribed hereinabove, and as defined in the appended claims.

We claim: A

1. A fatty material normally subject to oxidation stabilized with anuclearly alkylated S-hydroxy indole wherein each alkyl group containsfrom 1 to 4 carbon atoms.

2. A hydrocarbon normally subject to oxidation stabilized with anuclearly alkylated 5-hydroxyindole wherein each alkyl group containsfrom 1 to 4 carbon atoms.

3. A composition of material comprising a normally oxidizable materialstabilized with 2-alkyl-5-hydroxyindole wherein the alkyl group containsfrom 1 to 4 carbon atoms.

4. A composition of matter comprising a normally oxidizable materialstabilized with a 2,6-dia1ky1-5-hy- References Cited in the file of thispatent droxyindole wherein each alkyl group contains from 1 UNITEDSTATES PATENTS to 4 carbon atoms.

5- A fatty triglyceride normally subject to oxidation g a g i r istabilized with 2 -methyl-5-hydroxyindole. 5 2,521,415 5: 2a 3 "8:1 5:1950 6. A fatty triglyceride normally SUbJGCt to oxidation 2,559,907 vanLate et a1 July 10 1951 stabilized with 2,6-dimethyl5-hydroxyindole.

7. Lard stabilized with 2-methyl-5-hydroxyindole. 8. Lard stabilizedwith 2,6-dimethyl-S-hydroxyindole. OTHER REFERENCES 9. A hydrocarbonstabilized with 2,6-dimethyl-5-hy- 10 Chemical Reviews, vol. 30, pages69 to 96 (1942), page droxyindole. 86 only used.

10. Ahydrocarbon stabilized with Z-methyl-S-hydroxy- Jr. Chem. Soc.(London), 1948, pages 1605 to 1609, indole. page 1609 only used.

11. Gasoline stabilized with Z-methyl-S-hydroxyindole. Jr. Biol. Chem.,vol. 180, pages 961 to 967 (1949),

12. Gasoline stabilized with 2,6-dimethyl-5-hydroxy- 15 page 967 onlyused. indole. Beilstein, 4th edition, Band XXI, 1st Supp., page 218.

1. A FATTY MATAERIAL NORMALLY SUBJECT TO OXIDATION STABILIZED WITH ANUCLEARLY ALKYLATED 5-HYDROXY INDOLE WHEREIN EACH ALKYL GROUP CONTAINSFROM 1 TO 4 CARABON ATOMS.